In piston machines, in particular in lubricated compressors, a reliable lubrication in all lubrication points is extremely important for achieving a reliable operation. Usually, in each compressor package and in each cylinder one or more lubrication points are provided, which are supplied by a central lubrication system. The feeding of the lubrication points is usually provided by “pump-to-point” or “divider block” systems. In “pump-to-point” systems, the corresponding quantity of oil is directly supplied by the piston stroke of the respective pump element to the lubrication point. In the “divider block” system, the oil quantity supplied by the piston stroke of a central pump unit is divided by a so called “divider block” and supplied to the individual lubrication points.
However, known lubrication systems, in particular the “pump-to-point” systems, suffer from excessive inaccuracies in the setting of a low lubrication quantity.
An improved control of the lubricant supply may be obtained by lubrication systems with a common centrally pressure-controlled oil supply conduit, wherein the lubrication quantity is dosed for each lubrication point with a separate valve. Such a lubrication system is disclosed, for example, in EP 0049603 A2.
However, in such systems, besides the pressure controlled lubricant supply line, a leakage recirculation and/or overpressure-reducing line is required. This causes reliability problems and prevents a precise, controllable and monitored dosing of the lubrication quantity.
WO 2012/126473 A2 discloses a lubrication system for large cylinders, wherein, through lubricant injectors, lubrication oil is dosed into the cylinders. The system has a flow measurement for each lubricant injector.
EP 2484875 A1 discloses a lubrication system for large cylinders, wherein the quantity of lubrication oil provided by a lubricant injector is controlled by electromagnetic valves. In order to render the dosage independent from viscosity changes, the lubricant injectors are heated by heating elements.
Fundamentally, the lubricant quantity may be significantly reduced in almost all compressors, if it were possible to ensure that a reduced lubricant quantity securely reaches the lubrication point. However, the manufacturers of compressors keep themselves on the safe side and provide compressors with high lubrication rates. This causes high operating costs due to the lubricant consumption and problems with high oil quantities in the gas. This is particularly problematic in chemical plants and oil has to be onerously removed from the gas. In case of unmanned compressor stations in gas fields the lubrication oil has to be supplied the whole year long with corresponding high costs. In combustion machines, excessive lubricant quantities deteriorate in particular the combustion process and cause a higher emission of pollutants.
A reduction of the lubrication quantity is therefore desirable among other things also due to ecological and economic reasons. It is also desirable to be able to automatically adapt the lubrication quantity individually for each lubrication point to current load conditions or run-in processes.